Many providers of telecommunications services, such as AT&T, maintain large networks of buried fiber-optic cables. Most buried fiber-optic cables have spices every three to five miles. At each splice location, the individual fibers and the metallic sheath of a cable segment are bonded to fibers and sheath, respectively, of another cable segment. A water-resistant metallic enclosure (i.e., a splice case) encloses the splice to protect it from moisture. Each splice case typically lies a distance 5-10 feet underground to protect the splice from possible damage. In practice, great efforts are made to insure each splice case is substantially water-tight. However, moisture can and does enter the splice case, adversely affecting the splice, and ultimately, the quality of the information transmitted by the cable.
Presently, various techniques exist for determining the degree of moisture present in a splice case. For example, an Optical Time Domain Reflectometer (OTDR) can measure the degree of light scattering in a fiber of an optical-fiber cable by transmitting light into one end of the fiber and then measuring the degree to which such light is reflected back to the OTDR. Significant moisture in a splice case will adversely affect the splice, and hence, the light transmission characteristics of the fiber, causing a measurable change in the light backscattering measured by the OTDR. Depending on the type of OTDR making the measurement, it is possible to establish the relative location of a moisture-affected splice in the cable. Alternatively, the splice case may include a mechanical device, such as a bimetallic arrangement in contact with a fiber, for altering the characteristics of the light transmitted through that fiber in response to the level of moisture in the splice case. The variation in the characteristics of the light transmitted through the fiber may also establish the relative location of the moisture-containing splice case.
The above-described techniques for determining the relative level of moisture in a splice case require equipment at a cable termination point, such as a central office or the like, for detecting the variation in the characteristics of the light transmitted through a fiber in the cable. Even assuming the ability of such equipment to accurately establish the relative location of a moisture-affected splice case, such location information is often of limited value to a field technician. Even with such information, the technician must still must manually locate the cable to precisely establish the location of the moisture-affected splice case. Moreover, with the above-described technique, the field technician must communicate with a member of the On-Site Work Force (OWSF) following a measurement by the OTDR, or such other office-based equipment, to learn of a possible impairment of the transmission characteristics of the cable to detect a moisture-affected splice. In the absence of any such communication, a field technician undertaking a routine inspection of a buried fiber-optical cable has no way of determining the relative level of moisture in a splice case.
Thus, there is a need for a technique for determining the level of moisture in a splice case that is not subject to the foregoing disadvantage.